__________ is regarded as a universal particle.

Electrons:

1. Electrons are negatively charged particles present in the extranuclear part of the atom.
2. They revolve around the nucleus in the definite path.
3. It is regarded as a universal particle because the electron's mass and charge remain constant for every atom of the element.
4. The mass of the electron is $9.1\times {10}^{-31}\mathrm{Kg}$ and the charge on the electron is $1.6\times {10}^{-19}\mathrm{C}$.

Hence, the electron is regarded as a universal particle.